Creating the right atmosphere

Wednesday, 02 December, 2009

The potato is a leading human staple diet in the world, with only maize, wheat and rice ahead of it. The pattern of potato consumption has changed over the past few years and it is increasingly common for the potato to get to homes not as a fresh product, but processed in some form or other.

From the harvest to their marketing, vegetable products suffer damage produced by the triggering of a series of processes that tend to negatively affect their quality. This tendency can be modulated by a number of control techniques for the surrounding conditions of the products, mainly the storage temperature, the relative humidity and the composition of the surrounding atmosphere.

The study of the effects of the composition of the atmosphere surrounding the processed potato was the objective of the PhD thesis defended by Mr Ignacio Ángel Angós Iturgaiz at the Public University of Navarre. His work concluded that an atmosphere rich in CO2 and with high concentrations of O2 enhances the quality of the minimally processed potato given that these factors slow down the loss processes of water and nutrients, and its change of colour (browning).

The proportion of oxygen was raised to 80%, compared to the 20.9% in the atmosphere we normally respire, while CO2 - with a residual presence - was increased to 20%. This combination achieved optimum results where all the processes of degradation of the minimally processed potato - from its processing to its end of useful life - were slowed down. During the period - a maximum of 14 days - in which the potato was refrigerated at a temperature of 4 °C, the loss of water, nutrients and texture was slower, as was the onset of discolouration.

New storage methods extend life of Japanese plums

Getting fresh plums to the marketplace has been a challenge for fruit producers. The short shelf life of Japanese and European plums limits export and shipping options - Japanese plums can typically be stored for only three to five weeks after harvesting. For years, researchers have tested a variety of techniques to extend the storage life of Japanese and European plums, including pre-harvest calcium application, post-harvest heat treatment, application of an edible coating, cold storage, and modified atmosphere storage. Results of the tests have been inconclusive and sporadic.

Ahmad Sattar Khan, a PhD student, and Dr Zora Singh, Associate Professor of Horticulture at the Muresk Institute, University of Technology in Perth, Western Australia, recently carried out a research project attempting to extend the post-harvest storage life of Japanese plums (Prunus salicina Lindl. cv. Tegan Blue). The study, published in the Journal of the American Society of Horticultural Science, tested the effects of modified atmosphere packaging (MAP) and the application of 1-methylcyclopropene (1-MCP), a fumigant, on Japanese plums, including the effects on the fruit’s dietary antioxidants and overall quality.

According to the report, a combination of modified atmosphere packaging and 1-MCP had been shown to extend the storage life of plums with varying results, depending on storage conditions and type of polyethylene film used under MA storage.

The long-term storage study garnered important new information that will allow fruit producers and exporters to extend the storage life of Japanese plums for up to seven weeks. The researchers concluded that “1-MCP application in combination with MAP can be used effectively to reduce the ethylene biosynthesis and fruit softening during cold storage and to extend the storage life up to seven weeks followed by eight days of ripening without any adverse effects on the quality of the fruit”.

Why pears may become brown during commercial storage

Internal browning of pears stored under low oxygen conditions is related to restricted gas exchange inside the fruit, according to a study published in March in the open-access journal PLoS Computational Biology. Researchers at the Catholic University of Leuven in Belgium suggest a computer model that can be used to improve long-term storage of fruit under controlled atmospheres.

Pears and other fleshy fruit are commercially stored under low oxygen conditions to extend their storage life for up to nine months. If the oxygen concentration in the storage atmosphere is too low, quality disorders such as internal browning may result, causing major economic losses. This disorder is known to be related to the complex mechanisms of gas exchange, respiration and fermentation in fruit. However, further conclusions are unavailable due to the lack of reliable methods to measure gas concentrations inside the fruit.

The team, led by Bart Nicolaï, has developed a comprehensive computer model to predict the oxygen concentration inside the pear. The model incorporates equations for gas transport as well as for the respiratory metabolism. The researchers found that extremely low oxygen concentrations can occur in the core of the pear, which eventually may lead to cell death and browning.

While the model was developed for pears, the model is generic. Application to other fleshy fruit and plant organs is straightforward, but the tissue properties and the geometry will need to be measured, Nicolaï says. Further advances require investigation of the internal microstructure of the tissue to explain differences in gas exchange properties and to quantify the cellular and intercellular pathways for gas exchange and the metabolic processes.

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